This invention relates generally to braking systems for motor vehicles, and more specifically, to a braking system having an electro-hydraulic apply system with isolation pistons and a four-wheel hydraulic failsafe brake circuit.
Braking systems commonly known as brake-by-wire (BBW) typically include a brake pedal that does not directly communicate hydraulic pressure to the wheel brakes. Such BBW systems rely on automatic electric or electric-hydraulic means to remotely activate the brakes. In one type of electro-hydraulic braking system, the brake pedal does not communicate directly with the wheel brakes in normal mode. Instead, the hydraulic connection is blocked by solenoid-acutated isolation valves. The driver""s braking intent is communicated to the Electronic Control Unit (ECU) through various sensors built into the pedal feel emulator and master cylinder assemblies. The ECU processes the signals and sends subsequent commands to the hydraulic modulator to generate the desired wheel pressures. However, in failsafe mode, the wheel brakes are in direct hydraulic communication with a master cylinder.
The present invention is an isolation piston assembly comprising a cylinder, a piston, and a pair of hydraulic lines. The cylinder has only two apertures, and the piston is disposed in the cylinder. The first hydraulic line communicates between a wheel brake and a first side of the piston through one of the apertures. The second hydraulic line communicates between an accumulator and a second side of the piston through the other of the apertures.
One object of the present invention is to provide an isolation piston assembly of the type described above that has only a single seal.
Another object of the present invention is to provide a braking circuit including an isolation piston assembly of the type described above that has a four-wheel hydraulic failsafe mode for either front/rear or diagonal split base brake systems.
Still another object of the present invention is to provide a compact, simplified, easy to manufacture and robust braking system.